1. Field of the Invention
The invention relates generally to energy saving devices and methods for HVAC systems and particularly to a HVAC (Heating Ventilating and Air Conditioning) energy saving controller (ESC) to:
A) Predict and extend the fan run time of HVAC systems after the heating or cooling unit has shut off and/or
B) Stop the compressor or heater for a short duration of time, with the fan still blowing, if the compressor or heater has been running continuously for fixed or variable periods of time.
D) To modulate the gas furnace blower fan so that it alternates between low speed and high speed on a continuously basis in the same cycle, and
E) The ability to shut off or bypass the ESC in extreme temperatures by determining where the ESC is installed using a low-cost temperature sensor embedded into the ESC.
2. Description of the Related Art
Conventional HVAC (Heating Ventilating and Air Conditioning) systems include temperature changing components for changing the temperature and condition of air. Indoor air handlers drive air from the temperature changing component through supply ducts to zones within a building. A typical HVAC consists of a heating unit, an air conditioning or cooling unit or heat pump unit, and the fan blower at the air handler unit. A thermostat is used to control the conditions of the air in a conditioned space by sending control signals to the HVAC's high voltage relays or contactors to activate or deactivate one or more of the temperature changing components.
Conventional HVAC fan controllers typically run the ventilation blower fan for an additional 0 second to 90 seconds after the heater or air conditional compressor has been turned off. For example, most furnace heat exchangers are still hot (above 135 to 210 degrees F.) after the furnace fan turns off. This wasted energy is not delivered to the conditioned space when the fan stops blowing. The ESC recovers the remaining heat energy from the hot furnace heat exchanger after the furnace turns off and delivers this heat to the conditioned space. The ESC works by hijacking the fan control signals emitted by the thermostat and replace it with the new fan control signal emitted by the ESC itself. In this way, the HVAC fan controller only receives the fan control signals from the ESC itself and not from the thermostat directly. When the thermostat sends out the fan activate or deactivate command signal, it goes only to the ESC. The ESC reads this command and commands from the other environmental conditions plus from the HVAC components and computes the additional fan run time. Then, the ESC sends the adjusted command signal to the HVAC fan controller requesting it to run for a predicted additional extended time. Therefore, the ESC depends on the fan command signal emitted by the thermostat as source of input. The command signal of a thermostat is either a high of 24 vac or 0 vac (ground). Correspondingly, the ESC accepts either 24 vac or 0 Vac as its inputs.
For the ESC to work universally, it has to interface with every manufacturer of thermostats used in HVAC system. There are many manufacturers of thermostats where the fan output command signal goes into a floating or unknown state when the thermostat is shut off by putting the thermostat switch to system off. In such a case, if an ESC is connected to the thermostat, the fan command signal being in to unknown state could be read in as ON state, and the ESC will turn the fan on and run continuously. Therefore, there is a need to have a circuit in the ESC circuitry to read any unknown or floating signals from the thermostat fan command signal as known 24 vac or 0 vac state. In this way, the fan will always be turned off when it is not at an ON state.
Studies have shown that even after this built-in short additional fan run extension, the furnace surface and the air conditioner cooling coil still have some energy left.
Studies have also shown that if the cooling unit has been running continuously for a period of 20 minutes to 30 minutes, the cooling coil is wet and the evaporation of the water from the wet coil can provide additional cooling energy that can be harnessed. Also, if the heating unit has been running continuously for a period of approximately 20 to 30 minutes, the furnace is at its maximum temperature, and by shutting down the furnace for a short period of time while still allowing air flow through it, it will not only reduce the furnace temperature, therefore extending its life, but also harvest some residual heat energy for the conditioned room.
The ESC will adjust the fan operation automatically for heating based on gas furnace operating time or Heat Pump operating time. For air conditioning, the same ESC will adjust fan operation automatically for cooling based on air-conditioning compressor run time. The amount of time the fan continues to operate after the furnace is off or after the air conditional compressor is off, varies with the amount of time the furnace or compressor are running or not running using a microprocessor and firmware. The furnace additional fan run time indicates how much residual heat is left in the heat exchanger and the rate of temperature drop inside the room. The air conditioner compressor additional run time indicates how much cold water is condensed on the evaporator coil, and the rate of temperature rise inside the room. Hence, the ESC recovers and delivers left over residual energy to the conditioned space than is possible with original HVAC thermostat alone. The ESC improves the efficiency of HVAC equipment by delivering additional heating or cooling capacity for a small amount of additional electric energy (kWh).
For a subset of HVAC systems, where the heating element is a gas furnace, the thermostat setting is selected to “GAS.” In such applications, the thermostat will not energize the low voltage (24 Vac) fan output typically designated as the green wire. Instead the furnace control board controls the blower fan directly at the high voltage side of the blower fan contactor though an adjustable time delay relay or thermal switch. There are many types of blower fan motors in used in the HVAC industry. A popular type is a fan blower that uses a motor with variable speed. Another popular type is a fan blower motor that uses a fixed single speed. Yet another popular type is a fan blower motor that uses fixed multiple speeds such as low speed for the heat cycle and high speed for the cool cycle. For fan blower motors with 2 fixed speeds, the motor has 2 electrical tabs, one tab connected to energize low speed and another to energize high speed.
It has been shown by many studies that by using a variable speed blower fan, a better efficiency in the delivery of heats to the conditioned space can be achieved. However, replacing a multiple fixed speeds motor with a variable speed motor is expensive. Since the thermostat fan 24 Vac output controls the relay connections to high speeds tap of the blower fan motor, it is possible to vary the speed of the blower fan speed over the same heating cycle by pulsing the ESC's 24 Vac fan output so that it alternates from activation and de-activation of this fan line input into the 24 Vac relay control coil. This will have the effect of turning on a higher speed when the thermostat fan signal (green wire) is activated and defaulting to lower speeds when the thermostat fan signal is de-activated during the same gas heating cycle. This is a low-cost solution to replacing a multi-fixed speed blower fan motor with a more energy efficient variable speed blower fan motor.
While extending the fan run time after the heater or air conditioner has turned off and/or resting the compressor after 30 minutes or more of continuous runs may save energy, it may also cause discomfort to the occupants or users when the outside air temperatures are very high or very low. For example, during the peak of summer, the outside air temperature in some parts of the country could be over 120 degrees F. Similarly, during the very cold winter, the outside air temperature could be at −40 degrees F. In such cases, it will cause discomfort to the occupants with the fan extension run time which may be blowing hot air or cold air into the conditioned space.
Therefore, there is a need for an energy saving controller to have the ability to bypass or disable the fan extension or compressor rest when the outside air temperatures are at its extremes such as a heat wave during the summer or a cold front moving in during the winter.
There is also a need for an energy saving controller that can easily be inserted between the thermostat and the air handler of an HVAC system to recover additional heating and cooling capacity and operate the HVAC equipment at a higher efficiency with the ability to vary the furnace blower fan speed for even more efficiency, plus the ability to shut off the fan extension's run time and compressor's rest time during those times when the outside air temperatures are at its extremes.
There are many manufacturers of thermostats where the fan output command signal goes into a floating or unknown state when the thermostat is shut off by putting the thermostat switch to system off. In many cases, when the thermostat malfunctions, one of more of its outputs goes into a high impedance state or a float state or open circuit. When a thermostat is connected directly to the air handler unit, a high impedance state or a float state will not activate the HVAC relays or contactors and therefore, the HVAC system will remain off.
There are products in the market that are connected between the thermostat and the air handler unit controllers that cannot handle a floating state as inputs. A common case is the thermostat fan output signal being in unknown state when the thermostat is switched to OFF. These products would read this as ON state, and will turn the fan on and run continuously.
Therefore, there is a need to have a circuit to read any unknown or floating signals from the thermostat fan, cool or heat command signal as known 24 Vac or 0 Vac state. In this way, the fan, compressor or heater will always be turned off when it is not at an ON state. Further, it would be desirable to provide a low cost controller installed between the thermostat and the air handler that will work for the majority of the thermostats in the market, that it would solve the floating state of the thermostat output signal after the thermostat is turned off and keeps the HVAC in OFF state, and that could be easily installed and operated by the user.
Additionally, to minimize the limitations found in the prior art, there is a need for a ESC device that can be connected between an existing thermostat and the air handler of an HVAC system where the blower fan speed can be made to alternate between low speed and high speed on a continuous basis over the duration of the same gas furnace run time, and to extend to the fan run time after the gas furnace has shut down to blow the residual energy left at the furnace into the conditioned room. Additionally, there is a need to be able to bypass or disable the fan extension or compressor rest or heater rest when the temperature of the air outside is at its extremes.
The aspects or the problems and the associated solutions presented in this section could be or could have been pursued; they are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches presented in this section qualify as prior art merely by virtue of their presence in this section of the application.